Note: Descriptions are shown in the official language in which they were submitted.
5
Multilayer body and method for producing same
The invention relates to a method for producing a multilayer body, a
multilayer
body produced in this way, as well as a security element with such a
multilayer
body.
It is known to use thin-film systems in multilayer bodies which are used as
security elements. For this, a semi-transparent metal layer, a transparent
spacer layer and a second opaque metal layer are applied to a substrate by
vacuum deposition, with the result that a so-called Fabry-Perot system is
obtained which displays a color change effect when the angle of observation or
illumination is changed. The substrate can be, for example, a self-supporting
single-layered or multilayer film, which can have still further applied
layers, for
example varnish layers.
Investigations have now shown that the color change effect of such a security
feature displays almost the same color impression over the entire area when
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observed perpendicularly or at relatively acute observation angles a of from
approx. 0 to 20 , even if a surface relief structure is molded into the
substrate
or into a varnish layer applied to the substrate.
By a surface relief structure is meant a surface relief in the form of a free-
form
surface which is formed in particular by structures with a lens-like design
generating a magnifying, demagnifying or distorting effect. A surface relief
structure is preferably formed by a surface relief in the form of a Fresnel
lens
structure.
The object of the present invention is to provide a multilayer body as well as
a
method for producing same, which guarantees an improved optical impression
and increased security.
This object is achieved by a method, by a multilayer body as well as by a
security document.
Such a method for producing a multilayer body comprises the steps of:
a) providing a substrate film with a replication layer;
b) molding a surface relief appearing to the observer in the form of a three-
dimensional free-form surface, which is formed in particular by structures
with a
lens-like design generating a magnifying, demagnifying or distorting effect,
into
a surface of the replication layer;
C) applying a first metal layer to the surface of the replication layer
forming the
surface relief;
d) wet-chemically applying an at least partially transparent spacer layer to
the
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first metal layer;
e) applying a second metal layer to the spacer layer,
wherein at least one of the two metal layers is formed semi-transparent.
Optionally, one of the two metal layers can be formed as an opaque mirror
layer.
A multilayer body is hereby obtained which has the following layer structure:
- a substrate film;
- a replication layer, applied to a surface of the substrate film, into the
surface of
which facing away from the substrate film a surface relief appearing to the
observer in the form of a three-dimensional free-form surface is introduced
which comprises in particular structures with a lens-like design generating a
magnifying, demagnifying or distorting effect;
- a first metal layer, which is arranged on the surface of the replication
layer
forming the surface relief;
- a wet-chemically applied, at least partially transparent spacer layer,
which is
applied to a surface of the first metal layer facing away from the replication
layer, and which optionally forms a further surface relief;
- a second metal layer, which is applied to a surface of the spacer layer
facing
away from the first metal layer, wherein at least one of the two metal layers
is
formed semi-transparent.
Optionally, one of the two metal layers can be formed as an opaque mirror
layer.
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A layer structure is thus obtained in which a thin-film system, formed of the
first
metal layer, the spacer layer and the second metal layer, is combined with a
surface relief. As the spacer layer is applied to the (metalized) surface
relief of
the replication layer, the two boundary surfaces of the spacer layer can thus
each form a surface relief. These two surface reliefs are more or less
correlated, as will be explained in the following.
If the transparent spacer layer is applied wet-chemically, the surface relief
which
forms in the surface of the transparent spacer layer facing away from the
replication layer is present preferably relaxed ¨ thus weakened. The
correlation
of the two surface reliefs thus decreases.
In particular the structure depth in the further surface relief is reduced
compared
with the surface relief of the replication layer. How strongly relaxed, i.e.
weakened, the structures in the second boundary surface are depends, among
other things, on the wet-chemical coating parameters, in particular the
viscosity
and polarity, as well as the material system, in particular polymer system, of
the
varnish system used, but also the solvents used. The wet and the dry layer
thicknesses also have a significant influence.
Furthermore, measurements have shown that not only does the structure depth
at the second boundary surface decrease, but the shape of the structures can
sometimes also change. If, for example, a Fresnel structure with blazed
grating
is introduced into the replication layer, it could thus be shown that the
Fresnel
structures at the second boundary surface are present not only less deep, but
rather also sinusoidal.
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Because of the shape change of the further surface relief compared with the
surface relief of the replication layer, the resulting spacer layer between
these
two surface reliefs thus has a variable layer thickness. As the color
impression
of a thin-film system is determined by the layer thickness, a multilayer body
the
color of which changes over its surface is thus obtained. In particular, color
gradients or also color-to-gray gradients can thus be realized. Here and in
the
following, "gray" is to stand for uncolored or else achromatic.
Different optical effects can additionally be realized by the free-form
surface of
the surface relief, for example the formation of letters, numbers, but also
any
other objects which appear to protrude from the surface virtually or to dip
behind
the surface virtually. Further examples of the objects that can be represented
are schematized mountains, country outlines, animals, plants or plant parts
such as leaves or also buildings, bridges, gates as well as faces or
portraits, in
particular of famous personalities, etc. Furthermore, e.g., logos which appear
as
if they were bulging out and/or set back vis-à-vis the substrate surface, i.e.
as if
a domed surface were present in the area of the free-form surface, can be
generated. The objects thus obtain spatial depth, wherein particularly
characteristic optical effects which greatly increase the memorability and
thus
the identification effect of corresponding optically variable elements
precisely in
combination with the color variation generated by the thin-film system can
additionally be achieved in the case of suitable formation and arrangement of
partial areas with a lens-like design.
Such a multilayer body can be attached to a security document, which is
preferably formed as a banknote, identification document, visa document,
credit
card, drivers license or the like. In this way, a visually appealing security
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document that at the same time has a particularly good protection against
forgery is obtained.
By an at least partially transparent spacer layer is meant here a layer with a
transmittance or transmission of at least 50%, preferably at least 75% and
particularly preferably at least 90%. The data are understood as the average
of
the transmittance or transmission over the visible wavelength range from
430 nm to 690 nm. The wavelengths visible to humans lie in the range between
380 nm and 780 nm of the electromagnetic spectrum, wherein the relative
sensitivity of the eye in photopic vision below 430 nm and above 690 nm is
typically less than 1% of the maximum value at 555 nm.
In a preferred embodiment the spacer layer is applied by gravure printing,
curtain coating, slot coating, spin coating or dip coating. By means of the
named
methods, liquid media, in particular varnishes, can be reliably applied with a
predetermined wet layer thickness. Some wet-chemical methods for applying
the spacer layer are suitable for generating spacer layers with a layer
thickness
that varies in a locally targeted manner. For example, in the case of gravure
printing, this local variation can be realized by varying the ink cell
parameters on
the printing roller. This makes it possible to generate two- or multi-colored
effects in a targeted manner. Furthermore, with some wet-chemical methods
the spacer layer can be applied not only over the whole surface, but also
partially.
The spacer layer is preferably generated by applying a varnish, in particular
based on one of the following material or polymer systems, in order thus to
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achieve the desired optical properties: nitrocellulose, epoxy, polyester,
rosin,
acrylate, alkyd, melamine, PVA, PVC, isocyanate or urethane systems. The
varnish can also consist of a mixture of two or more of the material or
polymer
systems.
Further properties of such varnishes, such as for example the viscosity or
polarity, can be set to desired and advantageous values through suitable
additives. Furthermore, invisible security features can also additionally be
added through additives. For example, UV- or IR-active luminescent dyes, in
particular fluorescent dyes, can be added to the varnishes.
It is furthermore expedient if a varnish with a viscosity of from 5 mPa.s to
250 mPa.s, preferably from 15 mPa.s to 200 mPa-s and particularly preferably
between 20 and 170 mPa.s, is used for the application of the spacer layer.
With respect to the polarity of the varnish it is advantageous if the solvents
of
the varnish consist of solvents with a polarity index greater than 3.0 at a
rate of
at least 30% by mass, preferably of solvents with a polarity index greater
than
3.0 at a rate of at least 50% by mass. The polarity index is understood here
as
in Table 2 of EP 2264491 Al.
The wet-chemical coating parameters, in particular the viscosity and polarity,
as
well as the material system, in particular polymer system, of the varnish
used,
but also the solvent used can influence how strongly the surface relief of the
replication layer is reproduced in the surface of the spacer layer. This can
influence the optical properties of the thin-film system described at the
beginning.
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The spacer layer is preferably applied with a wet layer thickness of from 1 pm
to
20 pm, preferably from 2 pm to 10 pm. Both the wet and the dry layer
thicknesses also influence the resulting structure depth of the relief forming
in
the side of the spacer layer facing away from the replication layer and thus
the
optical properties of the resulting thin-film system.
Furthermore it is expedient if the spacer layer is dried after application, in
particular at a temperature of from 40 C to 200 C, preferably from 40 C to
150 C. There is preferably a temperature gradient in the dryer of the printing
machine, wherein the temperature is between 40 C and 60 C at the start of the
dryer and increases to 100 C to 150 C at the end of the dryer.
A controlled evaporation as well as a controlled curing of the varnish of the
spacer layer is hereby guaranteed with, simultaneously, sufficient time for
the
relaxation of the surface of the spacer layer, which also has an influence on
the
resulting surface relief and makes a process-stable manufacture of the
multilayer body with constant quality possible.
By a semi-transparent metal layer is meant a metal layer with a transmittance
or
transmission of at least 10%. It preferably lies between 20% and 80%,
particularly preferably between 25% and 65%. Alternatively, the optical
density
OD is often stated instead of the transmission. The optical density is less
than
or equal to 1.0 in the case of the semi-transparent metal layers. It
preferably lies
between 0.7 and 0.1 and particularly preferably between 0.6 and 0.18. At the
same time the reflectivity of the semi-transparent metal layer is further
preferably at least 10% and preferably more than 15%. The data are
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understood as the average of the transmittance or transmission as well as the
reflectivity over the visible wavelength range from 430 nm to 690 nm.
It is furthermore preferred if the semi-transparent metal layer is generated
by
vacuum deposition of Cr, Al, Cu, Ti, Ni, Ag or alloys with these metals such
as
e.g. A196%Cu4% or Inconel, in particular with a layer thickness of from 2 nm
to
20 nm, preferably from 4 nm to 15 nm.
By an opaque mirror layer is meant a metal layer with a reflectivity of at
least
60%, preferably more than 70% and particularly preferably more than 80%. A
transmission of the opaque metal layer of less than 10%, preferably less than
5%, is further preferred.
Furthermore it is preferred if the opaque mirror layer is generated by vacuum
deposition of Al, Cr, Ag, Cu, or alloys with these metals such as e.g.
A196%Cu4%,
in particular with a layer thickness of from 15 nm to 100 nm, preferably from
nm to 60 nm.
The first metal layer and/or the second metal layer is expediently generated
by
20 vacuum coating or sputtering. A constant layer thickness and a good
optical
quality of the respective layer can hereby be ensured.
It is preferred if the first metal layer and/or the second metal layer is
partially
demetalized, in particular by etching and/or lift-off. In the case of
structuring by
etching, after application of the respective metal layer an etch resist is
printed
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onto the first and/or second metal layer and in the areas not covered by the
etch
resist the metal layer is removed by an etchant, for example a lye. The etch
resist can then be removed, but it can also remain in the multilayer body and
perform additional decorative functions, for example if it is a colored or
pigmented resist varnish.
The first metal layer and/or the second metal layer is preferably demetalized
such that a demetalized area of the metal layer and/or of the second metal
layer
forms a symbol, image, logo, alphanumeric character or a combination thereof.
Additional items of optical information or designs can hereby be introduced
into
the multilayer body.
It is further preferred if the first metal layer and the second metal layer
are
demetalized such that the demetalized areas overlap in the viewing direction
onto the surface normal of the plane spanned by the multilayer body.
Translucent designs can hereby be implemented. A security element designed
in this way allows the substrate of the security document to be seen in the
overlapping demetalized areas, e.g. the printed banknote substrate or also a
window element in the substrate.
It is furthermore expedient if the first metal layer and the second metal
layer are
demetalized such that a metalized area of one of the metal layers overlaps the
outer contour of a demetalized area of the respectively other metal layer.
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Positioning or registration errors of the outer contour can hereby be at least
partially covered by the respectively other metal layer, with the result that
an
appealing design that appears register-accurate results without a high outlay
on
positioning. By register accuracy or registration accuracy is meant a relative
positional accuracy between two elements, e.g. areas or layers relative to
each
other. This positional accuracy can be set by means of so-called register
marks
or registration marks, which are specifically formed such that the respective
tolerance of the positional accuracy can in particular be read optically
particularly well or detected by machine. These register marks or registration
marks can represent separate elements, which are arranged, for example, in an
edge area. These register marks or registration marks can, however, also
represent integral components of the multilayer body which make it possible to
optically detect clearly, e.g., characteristic contours of a motif or
structures of
the motif or structures of the surface relief or similar.
It is advantageous if the surface relief and the further surface relief at the
two
boundary surfaces of the spacer layer at least partially correlate.
By an at least partial correlation of the reliefs is meant that the reliefs
are
similar, but not identical, and in particular can be transferred into each
other
through an imaging function, for example a compression. In the simplest case
the surface reliefs thus have the same structure, but different relief depths.
The
peaks or troughs of the relief structures further preferably lie on top of
each
other in each case, i.e. the peaks of the surface relief in the boundary
surface
between the replication layer and the first metal layer, seen vertically, lie
on top
of the peaks of the surface relief in the boundary surface between the spacer
layer and the second metal layer.
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As explained at the beginning, however, structural differences are also
possible,
such as for example a rounding off of a blazed grating into a more sinusoidal
cross-sectional structure. As already stated, the desired properties of the
multilayer body are made possible precisely through this partial correlation,
with
the result that color progressions or color-to-gray gradients are made
possible
in the appearance of the multilayer body.
It is particularly advantageous if a structure depth of the further surface
relief is
at most 90%, preferably 80%, further preferably at most 50%, of a structure
depth of the surface relief.
If the structure depth of the further surface relief is more than 50% of the
structure depth of the surface relief, a color-to-gray gradient appears in the
appearance of the multilayer body, otherwise a progression between two colors
results.
The structure depth of the surface relief can lie between 200 nm and 20 pm.
The structure depth of the surface relief is preferably 200 nm to 2000 nm,
preferably 300 nm to 1500 nm. These depth ranges are particularly suitable, in
combination with the preferred values for the average dry layer thickness of
the
spacer layer described below, for achieving the desired optical effects.
It is furthermore preferred if the spacer layer has an average dry layer
thickness
of from 200 nm to 800 nm, preferably from 300 nm to 700 nm, wherein the dry
layer thickness can be variable in the lateral direction.
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The local dry layer thickness d, together with the refractive index n of the
spacer
layer as well as the observation angle a, determines the resulting color
impression. With a refractive index of 1.5 and an observation angle of 300,
for
example a red color impression results if the dry layer thickness is 425 nm, a
green color impression results if the thickness is 350 nm and a blue color
impression results if the thickness is 300 nm.
It is further preferred if the spacer layer has a refractive index of from
1.35 to
1.65, preferably of approximately 1.5. As already explained, the color
impression of the multilayer body can be set through the interplay of
refractive
index and dry layer thickness.
The surface relief advantageously has microstructures with a depth-to-width
ratio of less than 0.5, preferably of less than 0.4. The microstructures can
be
refractive ¨ e.g. micromirrors ¨ or diffractive ¨ e.g. Fresnel-type
diffraction
gratings ¨ microstructures. By width of the microstructures is meant here the
distance from peak to peak or the period of the micromirrors or the
diffractive
microstructures.
The surface relief in the form of a free-form surface is preferably formed as
a
diffractive free-form element with a grating structure.
It is advantageous if the grating structure comprises grating lines
substantially
following the outlines of the free-form surface, wherein the distance between
the
grating lines and/or the grating depth changes over the grating structure and
in
particular changes continuously from the central area of the free-form surface
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out towards its edge. The period ¨ i.e. the distance between the grating lines
¨
and/or the depth of the surface relief varies in order to represent the
desired
free-form surface. Therefore it is further preferred if the depth-to-width
ratio in at
least 80% of the surface area of the free-form surface is less than 0.3. The
grating lines can, but do not have to, continuously follow the outlines of the
free-
form surface. They can also be interrupted, in particular interrupted with a
random pattern, e.g. in order to add a scattering action to the effect of the
grating structure. This can increase the observation angle for the overall
effect.
The grating structure can also be alternatively or additionally superimposed
with
a structure scattering in a mat way. Both interrupted grating lines and the
superimposition with a structure scattering in a mat way can lead to a more
achromatic appearance of the grating structure ¨ not of the thin-film system.
Through such a combination of a free-form surface with a grating structure, a
diffractive lens effect can be achieved which gives the multilayer body the
desired appearance. A special feature of the diffractive free-form elements
formed by grating structures is to be seen in the fact that such diffractive
lens
structures ¨ unlike refractive lenses ¨ generate a different visual impression
depending on the light wavelength used for the illumination or observation of
the
object in each case, whereby in turn particular design or security effects can
be
achieved.
It is preferred if a period of the grating lines at least in a partial area of
the
grating structure is smaller than 50 pm, preferably smaller than 30 pm,
particularly preferably smaller than 15 pm.
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The local dry layer thickness can be influenced in particular by a variation
of the
period. In the case of a varnish system which leads to a decoupling of the
boundary surfaces ¨ thus of the two surface reliefs - a further effect can
also
occur in addition to the shape change or shape leveling. Presumably, during
the
drying process of the wet-chemically applied spacer layer, capillary forces
which
originate from the grating grooves of the surface relief push material of the
spacer layer in the direction of a larger period of the structures ¨ typically
in the
direction of the center of the surface relief. The dry layer thickness is
thereby
greater in the center, or in areas with a coarse period Ax, than at the edge,
or in
areas with a smaller period Ax of the relief structures. The resulting color
gradient is continuous and perfectly registered relative to the shape of the
surface relief. The area with the second color typically starts when the
period of
the microstructures is 530 pm, preferably 520 pm, in particular 515 pm.
It is further preferred if the substrate film consists of a flexible plastic
film. For
example, the substrate film consists of PET, PEN, MOPP, PP, PA, PC, COC or
PVC.
The substrate film expediently has a layer thickness of from 4 pm to 500 pm,
preferably from 8 pm to 150 pm and particularly preferably from 12 pm to
50 pm.
It is further advantageous if the multilayer body has at least one further
translucent varnish layer, which is dyed by means of at least one dye and/or
pigment. The at least one dye is preferably a soluble dye or luminescent
substance. Dyes from the following substance groups are preferably used:
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metal complex dyes, in particular with Cr3+ or Co2+ as the central atom.
Examples are the Neozapon dyes from BASF and Orasol dyes from BASF
(formerly CIBA).
Further color effects can hereby be achieved, or the color effects of the thin-
film
system can be filtered and modulated. For example, a red color impression of
the thin-film system can be modulated to an orange color impression through a
translucent varnish layer dyed yellow.
It is expedient in particular if the at least one further varnish layer is
arranged
between the replication layer and the substrate film.
Additionally or alternatively, the replication layer can also be dyed by means
of
a dye and/or pigment, in order also to generate the named color effects.
Additionally or alternatively, the surface relief in the form of a free-form
surface
can also be combined with structures generating other effects. For example,
the
surface relief can also be gridded with a 2D, or 2D/3D or 3D hologram, in
particular combined in an interlaced arrangement, which represents a number
floating over the free-form surface. The proportion of surface area of the
structures generating other effects is preferably small, in order to influence
the
color effect of the surface relief in the form of a free-form surface in
combination
with the thin-film setup as little as possible. The proportion of surface area
is
preferably less than 30%, particularly preferably less than 20% and in
particular
preferably 510%.
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The multilayer body can be implemented as a transfer film or as a laminating
film. In the case of a transfer film the substrate film is joined to the
remaining
layers of the multilayer body, which form a transfer ply, by means of a
detachment layer. In the case of the application of the multilayer body to a
substrate, the multilayer body is secured, in particular glued, to the
substrate
and then the substrate film is peeled off the applied transfer ply. The
application
to the substrate can be effected, for example, by means of hot embossing or by
means of cold embossing. In the case of a laminating film, the substrate film
also remains on the multilayer body after the application of the multilayer
body
to a substrate.
The invention and embodiments thereof are explained in more detail below with
reference to the drawing. There are shown in:
Fig. 1 a schematic illustration of the mode of operation of a Fabry-Perot
thin-film system according to the state of the art;
Fig. 2 a schematic representation of a three-dimensional free-form
surface in top view and in cross section;
Fig. 3 a schematic detail view of a surface relief which optically imitates
the three-dimensional free-form surface shown in Fig. 2 as well as
an enlarged section of the surface relief;
Fig. 4 a schematic sectional representation through a multilayer
body
with a surface relief and a thin-film system according to the state
of the art;
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Fig. 5 a schematic sectional representation through an embodiment
example of a multilayer body with a surface relief and a thin-film
system with a wet-chemically deposited spacer layer;
Fig. 6 a schematic sectional representation through a further
embodiment example of a multilayer body with a surface relief and
a thin-film system with a wet-chemically deposited spacer layer;
Fig. 7 a schematic sectional representation through a further
embodiment example of a multilayer body with a surface relief and
a thin-film system with a wet-chemically deposited spacer layer;
Fig. 8 a schematic sectional representation through a further
embodiment example of a multilayer body with a surface relief and
a thin-film system with a wet-chemically deposited spacer layer;
Fig. 9 reflection spectra of multilayer bodies with a surface
relief and a
thin-film system;
Fig. 10 a schematic sectional representation through a further
embodiment example of a multilayer body with a surface relief, a
color layer and a thin-film system with a wet-chemically deposited
spacer layer;
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Fig. 11 a schematic sectional representation through a further
embodiment example of a multilayer body with a surface relief, a
partial metal layer and a thin-film system with a wet-chemically
deposited spacer layer;
Fig. 12 a schematic view of a security document with a multilayer
body
according to Fig. 11;
Fig. 13 a schematic view of a motif realized by means of a
multilayer body
according to Fig. 11;
Fig. 14 a schematic representation of the method steps for producing
an
embodiment example of a multilayer body with partial
demetalization;
Fig. 15 a security element produced by means of a method according
to
Fig. 14 in front view;
Fig. 16 a schematic representation of the method steps for producing
an
alternative embodiment example of a multilayer body with partial
demetalization;
Fig. 17 a security element produced by means of a method according
to
Fig. 16 in front view;
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Fig. 18 a schematic representation of the method steps for producing
a
further alternative embodiment example of a multilayer body with
partial demetalization;
Fig. 19 a schematic representation of the method steps for producing a
further alternative embodiment example of a multilayer body with
partial demetalization.
A Fabry-Perot thin-film system 1 represented schematically in Fig. 1 consists
of
a semi-transparent layer 11, usually a first metal layer (e.g. Cr, Al, Cu, Ti,
Ag, Ni
or Inconel), a transparent spacer layer 12 (e.g. MgF2, SiO2 or a polymer
varnish) as well as a second metal layer 13. The latter likewise usually
consists
of metal (e.g. Al, Cr, Ag, Cu). It can be opaque or also semi-transparent. The
layers 11, 12, 13 are deposited onto a substrate film 2. The sequence of the
layers 11, 12 and 13 can also be reversed and the effect can be visible from
the
back, e.g. through a window of a security document.
Part of the light incident at the angle ain is reflected on the semi-
transparent first
metal layer 11, part is absorbed and part is transmitted. The transmitted part
penetrates the transparent spacer layer 12 and is reflected on the second
metal
layer 13. The reflected part of the light again penetrates the transparent
spacer
layer 12 and is partially transmitted through the semi-transparent layer 11.
This
transmitted part interferes with the portion of the light reflected on the
semi-
transparent layer 11 and reaches the eye of the observer at the angle aout,
wherein ain=aout=a. Light refraction was disregarded in this schematic
representation. Because of the interference of the light portions, the light
appears colored to the observer. The color impression here depends among
Date recue/Date received 2023-03-31
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other things on the thickness d as well as on the refractive index n of the
spacer
layer 12 and the angle a. Constructive interference occurs when the optical
path
difference A between the portion of the light reflected on the first metal
layer 11
and the portion of the light reflected on the second metal layer 13 is a
multiple
of the wavelength X.
There are various coating methods which can be used to produce such a layer
system 1. The two metal layers 11, 13 are usually applied using vacuum
technology, e.g. by means of evaporation or sputtering. In contrast, the
transparent spacer layer 12 can on the one hand be applied using vacuum
technology, e.g. by means of thermal evaporation of MgF2. On the other hand,
such transparent layers 12 can also be produced wet-chemically, e.g. by means
of gravure printing or slot coating.
These different production methods lead to very similar results on smooth
substrates 2; a surface with a homogeneous color tilt effect or color change
effect is achieved. On structured surfaces, in contrast, wet-chemically
applied
transparent spacer layers 12 result in clearly different layer patterns from
spacer
layers 12 applied using vacuum technology. This is due to the fact, among
other
things, that layers applied using vacuum technology are built up piece by
piece,
while wet-chemically applied layers are usually applied all at once and the
liquid
layer only cures in the drying and/or curing process, e.g. UV curing.
Consequently, such thin-film systems 1 can be applied not only to the smooth
surfaces shown in Fig. 1, but also to structured surfaces. An example of this
is
shown in Fig. 2. Surface relief structures 3 generate a three-dimensional
surface which seems to protrude from the substrate plane. The shape of this 3D
surface can be chosen almost randomly (free-form). In Fig. 2 the surface
relief
Date recue/Date received 2023-03-31
22
structure 3 imitates a droplet with an optically three-dimensional effect as a
free-
form surface. The structures are a special variant of Fresnel lenses. Fig. 2a
shows a schematic top view of such a surface relief structure 3, which
imitates
the 3D droplet. An exemplary section through this three-dimensional shape is
indicated with A-A'.
Fig. 2b shows a schematic side view along the section A-A` through this three-
dimensional shape, wherein here the height profile 31 seemingly generated (not
really present) is represented in the z' direction.
Such a three-dimensional surface shape or an apparent height profile 31 can be
optically generated by Fresnel lens-type microstructures 32. Fig. 3a shows a
schematic side view (not to scale) of exemplary Fresnel-type relief structures
32
which optically generate the three-dimensional droplet shape from Fig. 2. For
simplification, only a few grooves of the Fresnel lens are represented. If the
representation were to scale, many more would have to be represented.
Furthermore, to simplify the representation, the z-scale is reproduced greatly
extended. In addition to the continuous Fresnel structures represented, so-
called binary Fresnel structures can also generate a similar effect. In other
words, the comparatively strongly 3D domed impression from Figs. 2a, 2b can
be simulated with special diffractive structures the extent of which in the z
direction can be significantly smaller than simulated by the achieved optical
effect.
Fig. 3b shows the area marked by a dotted circle in Fig. 3a enlarged and
represented approximately to scale. In the currently used hot-embossing films,
the smallest period or structure width AX`min of the surface relief structures
32 is
approx. 3 pm and thus is approximately two to three times larger than the
depth
Date recue/Date received 2023-03-31
23
tR. The average depth-to-width ratio of the structure elements is consequently
smaller than 0.5. Here the depth of the structures tR typically lies in the
range
from 500 nm to 1500 nm. The angles of the edges 321 of the relief structures
32
in reality are consequently much less acute than Fig. 3a shows.
A schematic cross section, not to scale, through a multilayer body 4 known
from
the state of the art is shown in Fig. 4. This comprises a substrate film 41
with a
replication layer 42, into which a surface relief 43 is introduced. To this,
in each
case using vacuum technology, a semi-transparent first metal layer 44, a
transparent spacer layer 45 and a second metal layer 46 are applied, which
form a thin-film system 47 of the described type. The replicated surface
relief 43
reproduces itself recognizably in the further layers. It is to be recognized
that
the replicated structures are present almost identically in the second
boundary
surface of the transparent spacer layer 45 ¨ thus the boundary surface between
the spacer layer 45 and the second metal layer 46. This is the case with
spacer
layers 45 applied purely using vacuum technology, as here these layers are
built up piece by piece. The structure depth 'tik on the side of the spacer
layer 45
opposite the replication varnish usually lies ¨ in the case of the typical
layer
thicknesses of the spacer layer 45 applied using vacuum technology ¨ in the
range from 90% to 100% of the original depth in the replication varnish tR.
The
peaks of the structures here can, however, also be present slightly rounded.
When observed perpendicularly or at relatively acute observation angles a of
from approx. 00 to 20 , the color effect of such a security feature -
consisting of
the relief structures 43 of the replication layer 42, coated with the thin-
film
system 47 - displays almost the same color impression over the entire area of
the relief structures, as the layer thickness overall is almost identical. The
thin-
film filter thus acts as in a flat ¨ i.e. unstructured ¨ area.
Date recue/Date received 2023-03-31
24
Fig. 5 shows, not to scale, an embodiment example of a multilayer body 5 which
combines a surface relief 51 with a thin-film system 52. The multilayer body 5
comprises a substrate film 53, which preferably consists of PET, PEN, MOPP,
PP, PA, PC, COC or PVC and has a layer thickness of from 4 pm to 500 pm,
preferably from 8 pm to 150 pm and particularly preferably from 12 pm to
50 pm.
A surface relief 51 is introduced into the substrate film 53 or into a
replication
layer applied to the substrate film 53. This is preferably formed as a
diffractive
free-form element with a grating structure.
It is advantageous if the grating structure comprises grating lines
substantially
following the outlines of the free-form surface, wherein the distance between
the
grating lines and/or the depths of the grating structure changes over the
grating
structure and in particular changes continuously from the central area of the
free-form surface out towards its edge.
Through such a combination of a free-form surface with a grating structure, a
diffractive lens effect can be achieved which gives the multilayer body the
desired appearance.
It is preferred if a period of the grating lines at least in a partial area of
the
grating structure is smaller than 50 pm, preferably smaller than 30 pm,
particularly preferably smaller than 15 pm.
Date recue/Date received 2023-03-31
25
A semi-transparent metal layer 54 is applied to the surface relief 51,
preferably
by vacuum coating, sputtering or the like. It is preferred if the metal layer
consists of Cr, Al, Cu, Ti, Ni, Ag or Inconel and has a layer thickness of
from
2 nm to 20 nm, preferably from 4 nm to 15 nm.
A transparent spacer layer 55 is applied to the side of the metal layer 54
facing
away from the surface relief 51 wet-chemically, in particular by means of
gravure printing, curtain coating, slot coating or the like.
The spacer layer 55 is preferably generated by application of a varnish, in
particular based on nitrocellulose, epoxy, polyester, rosin, acrylate, alkyd,
melamine, PVA, PVC, isocyanate or urethane systems, in order thus to
generate the desired optical properties.
The varnish can contain further additives, such as e.g. crosslinkers or
surfactants, in order to set its physico-chemical properties, such as for
example
the viscosity or polarity, to desired and advantageous values.
It is furthermore expedient if, for application of the spacer layer, a varnish
with a
viscosity of from 5 mPa-s to 250 mPa.s, preferably from 15 mPa.s to
200 mPa.s and particularly preferably between 20 mPa.s and 170 mPa.s is
used. With respect to the polarity of the varnish, it is advantageous if the
solvents of the varnish consist of solvent with a polarity index greater than
3.0 at
a rate of at least 30% by mass, preferably of solvent with a polarity index
greater than 3.0 at a rate of at least 50% by mass. The polarity index here is
understood as in Table 2 of EP 2264491 Al.
Date recue/Date received 2023-03-31
26
The surface relief 51 of the substrate film 53 reproduces itself on the side
of the
spacer layer 55 facing away from the surface relief 51. The wet-chemical
coating parameters, in particular the viscosity and polarity of the varnish
system
used, but also the varnish system used and/or the solvent or solvents, can
influence how strongly the surface relief 51 reproduces itself in the surface
551
of the spacer layer 55.
The spacer layer 55 is preferably applied with a wet layer thickness of from
1 pm to 20 pm, preferably from 2 pm to 10 pm. Both the wet and the dry layer
thicknesses also influence the resulting structure depth of the relief 552
forming
in the side of the spacer layer 55 facing away from the replication layer 53
and
thus the optical properties of the resulting thin-film system 52.
After the wet-chemical deposition, the spacer layer 55 is dried, in particular
at a
temperature of from 40 C to 200 C, preferably from 40 C to 150 C. There is
preferably a temperature gradient in the dryer of the printing machine,
wherein
the temperature is between 40 C and 60 C at the start of the dryer and
increases to 100 C to 150 C at the end of the dryer. This results in a
controlled
average dry layer thickness of from 200 nm to 800 nm, preferably from 300 nm
to 700 nm, with the desired degree of correlation between the two surface
reliefs 51, 552.
Finally, a second metal layer 56, preferably made of Al, Cr, Ag or Cu with a
preferred layer thickness of from 15 nm to 100 nm, particularly preferably
from
20 nm to 60 nm, is also deposited onto the side of the spacer layer 55 facing
away from the metal layer 54.
Date recue/Date received 2023-03-31
27
Because of the wet-chemical deposition, the structure depth tA of the surface
relief 552 reproduced in the spacer layer 55 decreases appreciably compared
with the structure depth tR of the surface relief 52 in the substrate film 53,
i.e. tA
80% tR. How strongly relaxed, i.e. weakened, the structures in the second
5 boundary surface are depends, among other things, on the wet-chemical
coating parameters, in particular the material base, the viscosity and the
polarity
of the varnish system used, but also the solvents used. The wet and the dry
layer thicknesses also have a significant influence.
Measurements have shown that not only does the structure depth in the relief
552 of the spacer layer 55 decrease, but the shape of the structures can
sometimes also change. Micrographs thus show that, for example, a blazed
shape of Fresnel structures present at the first boundary surface ¨ thus
between the semi-transparent metal layer 54 and the spacer layer 55 ¨ is
present not only less deep, but rather also sinusoidal at the second boundary
surface ¨ thus between the spacer layer 55 and the second metal layer 56. This
is represented schematically in Fig. 6.
Because of this shape leveling and/or the decreasing correlation between the
two surface reliefs 51, 552, the thickness of the spacer layer can vary
relatively
greatly, which then leads to a substantial weakening of the color contrast. As
the color impression is influenced directly by the layer thickness of the
spacer
layer 55, such a relatively greatly varying layer thickness results in a
greatly
varying color impression in a lateral extent in the size of the grating period
and
thus below the resolution limit of the human eye.
For example, at an observation angle of 30 , a layer thickness of the printed
spacer layer 55 (refractive index n=1.5) of 425 nm yields a red color
impression,
Date recue/Date received 2023-03-31
28
a thickness of 350 nm yields a green color impression and a thickness of
300 rim yields a blue color impression. The mixed color of such a spacer layer
55 with a layer thickness varying greatly below the resolution limit of the
human
eye therefore usually appears dark gray or metallic gray to the human eye. The
greatly varying layer thickness of the spacer layer 55 is mainly present with
a
fine grating period in areas of the relief structure 51, 552. In this case
there is a
gradient from color in areas with a coarse period of the relief structure
towards
gray/achromatic in areas with a fine period of the relief structure. As the
gradient is generated by the structures of the surface relief 51, the color-to-
gray
gradient is perfectly registered relative to the 3D impression or the three-
dimensional surface shape of the relief structures 51, 552.
The great variation of the layer thickness of the spacer layer 55 is mainly
present in regions in which the period of the surface relief microstructures
is
small ¨ i.e. 5_50 pm, preferably 530 pm, in particular 520 pm. The resulting
variation of the layer thickness of the spacer layer 55 results in a color-to-
gray
gradient, wherein the area appearing gray typically starts when the period of
the
surface relief microstructures is 550 pm, preferably 530 pm, in particular
520 pm. The color-to-gray gradient optically clearly emphasizes the free-form
surface.
The period of the microstructures is typically smaller towards the edge of the
free-form surface, which is why the color-to-gray gradient usually runs from
the
center of the free-form surface to the edge.
In addition to a color progression or color gradient from a first color to a
gray or
metallic impression, it is also possible to realize a progression from a first
to a
second color. For this it is preferred for the correlation of the two boundary
Date recue/Date received 2023-03-31
29
surfaces of the spacer layer 55 to be very small, i.e. tA 5 50% tR and in
particular
tA 5 30% tR. In the extreme case, the second boundary surface is even formed
almost smooth towards the second metal layer, or the correlation between the
surface reliefs 51, 552 is (almost) completely removed. This is an extreme
form
of the shape change or shape leveling. Figures 7 and 8 show this in schematic
side views that are not to scale.
In particular in the case of a varnish system which leads to a decoupling of
the
boundary surfaces, a further effect can also occur in addition to the shape
change or shape leveling. Presumably, during the drying process of the wet-
chemically applied spacer layer 55, capillary forces which originate from the
relief grooves push material of the spacer layer 55 in the direction of a
larger
period of the structures of the surface relief ¨ i.e. typically in the
direction of the
center of the relief shape or the desired free-form surface. Furthermore,
material of the spacer layer 55 is no doubt also pushed in the direction of
mirror
surfaces, surrounding the surface relief, or also surrounding surfaces with
flatter
other structures. Diffraction gratings with periods below 2 pm and grating
depths
below 200 nm are an example of these other structures. The layer thickness is
thereby larger in the center of the free-form surface, or in areas with a
coarse
period Ax, as well as in the areas surrounding the surface relief than at the
edge
of the free-form surface, or in areas with a smaller period Ax of the relief
structures. In areas with a relatively large local period Ax of the relief
structures
the layer thickness is almost identical to the thickness in areas without
structures, i.e. on a smooth surface, or almost identical to the thickness in
areas
with flatter other structures. The color gradient is continuous and perfectly
registered relative to the shape of the surface relief. The color gradient
thereby
optically clearly emphasizes the free-form surface. The area with the second
Date recue/Date received 2023-03-31
30
color typically starts when the period of the surface relief microstructures
is
530 pm, preferably 520 pm, in particular 515 pm.
Multilayer bodies in the manner of the invention, which have a gradient from a
first color to a second color, could even have two different color effects in
the
area with the surface relief in the form of a free-form surface. Thus, for
example
in the area with a coarse period Ax, there can be a color effect from red in
the
case of almost perpendicular observation to green in the case of tilted
observation (e.g. 30 ). At the same time, in the area with a fine period Ax,
there
can be a color effect from green in the case of almost perpendicular
observation
to blue in the case of tilted observation (e.g. 30 ).
As a whole, it is thus possible to realize both a color-to-gray and a color-to-
color
progression.
A color progression from a first color to a metallic/gray/achromatic
impression
occurs when the relaxation is less than 50%, i.e. when tA 50% tR. At the same
time, however, tA must be 5 90% tR and preferably tA 5 80% tR. In other words,
if
the structure depth at the boundary surface between the spacer layer and the
second metal layer lies between 50% and 90%, preferably 50% to 80%, of the
structure depth at the boundary surface between the spacer layer and the first
metal layer, a color/gray gradient results.
A color progression from a first to a second color occurs above all when the
structure depth relaxes by more than 50%, i.e. when tA 5 50% tR. tA 5 40% tR
is
preferred, tA 5 30% tR is further preferred and tA 5 20% tR is preferred in
particular. In other words, if the structure depth at the boundary surface
between the spacer layer and the second metal layer 55 is smaller than/equal
to
Date recue/Date received 2023-03-31
31
50%, preferably smaller than/equal to 40%, particularly preferably smaller
than/equal to 30% and in particular smaller than/equal to 20% of the structure
depth at the boundary surface between the spacer layer and the first metal
layer, a gradient between two colors results.
The described cases can be distinguished by means of spectrometer
measurements. Figs. 9A to 9C show examples of measured spectra in the case
of perpendicular incidence ¨ i.e. when a=0 ¨ for the case shown in Fig. 4 of
very strong correlation of the boundary surfaces in the case of a spacer layer
applied using vacuum technology according to the state of the art (Fig. 9A),
the
case shown in Fig. 5 of weakened correlation of the surface reliefs in the
case
of wet-chemical deposition of the spacer layer (Fig. 9B) and the case shown in
Fig. 7 of very low correlation of the surface reliefs in the case of likewise
wet-
chemical deposition of the spacer layer (Fig. 9C). One spectrum in the area
with
a coarse period of the surface relief (center, dashed-line graph) and one in
the
area with color gradient or in the area with a small period of the surface
reliefs
(edge, continuous-line graph) are shown in each case.
As shown in Fig. 9A, the spectra in the central and edge areas of the surface
relief in the case of a vapor-deposited spacer layer substantially follow the
same
progression ¨ i.e. the peak maxima and minima lie at the same wavelength. The
thin-film system therefore appears monochromatic over the entire area of the
free-form surface. The slightly reduced reflection in the edge area is due to
the
fact, among other things, that the surface relief diffracts part of the light
more
strongly out of the viewing direction of the spectrometer in the edge area
than in
the central area.
Date recue/Date received 2023-03-31
32
In Fig. 9B it is to be recognized that in the area of the surface relief 51
there is a
gradient from a first color (center, dashed-line graph) to a gray/metallic
impression (edge, continuous-line graph), wherein the difference AR between
the maximum Rmax and the minimum Rmin of the reflection measured in the case
of perpendicular incidence in the spectral range from 430 nm to 690 nm is at
least 3x, preferably at least 5x and in particular preferably at least 7x,
greater in
the area of the first color than in the area with the gray/metallic
impression.
In the case of Fig. 9C it is to be recognized that in the area of the surface
relief
51 there is a gradient from a first (center, dashed-line graph) to a second
color
(edge, continuous-line graph), wherein the two reflection spectra, belonging
to
the colors and measured in the case of perpendicular incidence, exhibit a
shift
of the wavelength AX, of at least one of the reflection peaks of at least 10
nm,
preferably at least 20 nm and in particular at least 30 nm. This reflection
peak
here usually lies in the spectral range from 430 nm to 690 nm. In the measured
example shown in Fig. 9c, the shift of the peak wavelength is AX = 531 nm ¨
508 nm = 23 nm.
Instead of the Fabry-Perot systems described up to now, other thin-film
systems
can also be used, e.g. HLH systems (HLH, LHL, HLHL, LHLH, etc.). A specific
example of this is a vapor deposition of the replicated surface structure with
a
layer of high-refractive-index material (H, H for high refractive index), e.g.
80 nm
TiO2 with n ge, 2.54 at X = 589 nm, ZrO2 or ZnS. A rather low-refractive-index
spacer layer (L, L for low refractive index) with the thickness d is then
applied
wet-chemically, e.g. 500 nm PVC varnish with n = 1.545 at X = 589 nm. This
layer generates the optical path difference for the interference of the light
portions. In this spacer layer the structures in the second boundary surface
are
again present relaxed, which leads to a gradient. As a third layer, again a
layer
Date recue/Date received 2023-03-31
33
of high-refractive-index material (H), e.g. 80 nm TiO2, ZrO2 or ZnS, is
applied,
e.g. vapor-deposited. The thickness of the high-refractive-index layers is
preferably in the range from 10 nm to 200 nm and in particular between 20 nm
and 100 nm. Such a thin-film system also generates, through interplay with the
relief structures, a color impression with a color progression or color
gradient.
The advantage of such a thin-film system is that it is transparent, and thus
can
also be placed over vital, in particular personalized and/or individualized,
data
for example in ID documents.
The color progression of the multilayer bodies 5 described up to now can also
be modified by means of color filters which, seen starting from the observer,
are
located above the thin-film stack. For example, in the layer stack, one or
more
layers can be dyed.
Fig. 10 shows, in a schematic side view, the example of a dyed multilayer body
5. The layer structure corresponds to that shown in Fig. 5. An additional dyed
varnish layer 58 with a preferred layer thickness of from 200 nm to 5 pm is
provided between the replication layer 53 and the substrate film 57.
Alternatively, the surface relief structure 51 can, however, also be
replicated
into a dyed replication varnish 53. The color impression of the surface relief
51
in all of these cases is superimposed with the color impression of the color
filter
58.
A specific example is a so-called gold foil, which has a replication varnish
53
indirectly or directly dyed yellow. In such a film, the background which is
deep
red for example at an observation angle of 30 as well as the deep red area of
the surface relief would appear more orange. The chrome-metallic edge area of
the surface relief on the other hand would have a dark yellow effect. The
color
Date recue/Date received 2023-03-31
34
gradient would therefore no longer be deep red to chrome-metallic, but orange
to yellow.
A specific example of the integration of the combination of surface relief 51
in
the form of a free-form surface and thin-film system 52 in the manner of the
invention into a security element 6 with a KINEGRAM is represented in Fig.
11.
Here a KINEGRAM design is replicated and vapor-deposited over the whole
surface with a first aluminum layer 61. Then, in a standard demetalizing
process, in register, the aluminum is removed in the area 62 with the surface
relief 51 as well as in the areas 63 where the thin-film effect is otherwise
still to
be seen. The thin-film system 52, which corresponds to the already described
embodiment examples, is then applied to the back, seen from the observer, of
the first aluminum layer 61.
Fig. 12 shows an exemplary model banknote 7 with such a demetalization
design. A security strip 71 contains, among other things, a surface relief 51,
which represents a free-form surface in the form of a lion and which has one
of
the described color gradients. This surface relief 51 is present in a
demetalized
area 62 of the strip. The rest of the strip has yet other effects, e.g.
diffractive
effects. Furthermore, the strip contains three demetalized areas 63 in the
form
of the number "55", wherein the Fabry-Perot three-layer system 52 is also
present in these demetalized areas. The three numbers "55" consequently
display the same or a very similar color tilt effect as is also present in the
surface relief 51 in areas with a coarse period. Alternatively, the color
effect in
the areas 63 can be different from that in the area 62. For this, a different
thickness of the spacer layer 55 must be present locally. In printing
processes it
is easily possible to generate locally different thicknesses in a targeted
manner.
Date recue/Date received 2023-03-31
35
This can be achieved, e.g., by different depths of the ink cells in a gravure
printing roller in the areas of the roller which deposit the spacer layer onto
the
areas 62 and 63.
A further alternative provides that the metal layers of the thin-film system
52 are
additionally removed in the areas 63 by means of one or more further
demetalizing steps. This can be achieved, e.g., via a so-called lift-off
process. In
this case, a color effect is present in the area 62, whereas the substrate is
to be
seen undisturbed by metal layers in the areas 63.
Fig. 13 shows a schematic top view of such a security element 71 in detail.
The
color progression in the area of the surface relief 51 is illustrated by
contour
lines. The background for the motif formed by the surface relief 51 is formed
by
metalized surfaces 72.
The color effect of the surface relief 51 in the form of a free-form surface
can, as
previously described, be visible from the front of the substrate, i.e. from
the side
to which the multilayer body is applied. Alternatively, the layer structure
can also
be designed such that the color effect is to be seen through a window in the
security document to which the multilayer body is applied. In other words, an
observer sees the color effect of the surface relief when he observes the back
of the security document. At the same time, the multilayer body can be
designed such that the observer sees the surface relief 51 in the form of a
free-
form surface in a metallically reflecting and spatially mirrored form on the
front
of the security document. The mirroring here can be not only a left/right
mirroring. The free-form surface can additionally also appear bulging out on
one
side of the security document and optically appear to be set back on the other
Date recue/Date received 2023-03-31
36
side. This increases the memorability and thus the identification effect
additionally.
Fig. 14 shows an alternative method for producing a multilayer body 5 with
partial demetalization of the metal layers 54, 56. A first metal layer 54, as
already explained, is here also applied to the substrate film 53 with a
surface
relief 51 of the described type. In this embodiment example, the first metal
layer
54 is formed as an opaque mirror layer. This is overprinted with an etch
resist 8,
which remains omitted in areas 541 to be demetalized. In these areas 541, the
metal layer 54 can then be removed by etching (Fig. 14A).
After the etching, the etch resist 8 can be removed again by suitable solvents
(Fig. 14B) and the uncovered metal layer 54 can be overprinted with the
transparent spacer layer (Fig. 14C).
Before the deposition of the second metal layer 56, a lift-off varnish 9 is
deposited onto the spacer layer 55 in those areas 561 in which the second
metal layer 56 is to be removed later (Fig. 14D). The second metal layer 56 is
then applied over the whole surface (Fig. 14E). In this example the second
metal layer is formed semi-transparent. When the lift-off varnish 9 is removed
by a suitable solvent, the second metal layer 56 is also removed with it in
the
areas 561 (Fig. 14F).
Demetalized areas 541 and 561 are thus obtained in the two metal layers,
which overlap and which can form a motif. There is no thin-film effect in the
demetalized areas 541 and 561.
If the multilayer body 5 is applied to a security document, for example a
banknote 7 by means of a suitable adhesive layer 57 (Fig. 14G), the
Date recue/Date received 2023-03-31
37
demetalized areas allow the substrate of the banknote to be viewed. The
demetalized area 541 forms, as is to be recognized in Fig. 15, the number
"55",
while the demetalized area 561 frames the surface relief.
The area of the surface relief 51 is arranged over a window 72 of the
banknote,
with the result that the effect of the surface relief 51 with the color change
effect
generated by the thin-film system 52 is to be recognized from the other side
of
the banknote 7. The demetalized areas 541 and 561, in contrast, are concealed
by the substrate of the banknote 7 in the case of observation through the
window 72.
Fig. 16 shows a further alternative method for producing a multilayer body 5
with partial demetalization of the metal layers 54, 56. A first metal layer
54, as
already explained, is here also applied to the substrate film 53 with a
surface
relief 51 of the described type. This is overprinted with an etch resist 8,
which
remains omitted in areas 541 to be demetalized. In these areas 541 the metal
layer 54 can then be removed by etching (Fig. 16A). In addition the area of
the
surface relief 51 also initially remains left open here. In this embodiment
the
etch resist 8 is not removed and can take on additional decorative functions.
Now a lift-off varnish 9 is printed on in the areas 541 to be left open (Fig.
16B).
Then a further, semi-transparent metal layer 58, preferably made of chromium,
is vapor-deposited over the whole surface (Fig. 16C) and removed again by
peeling off the lift-off varnish 9 in the areas 541 (Fig. 16D). The area of
the
surface relief 51 is thus now also metal ized.
Analogously to the already described methods, the spacer layer 55 is now
applied (Fig. 16E) and vapor-deposited over the whole surface with metal (Fig.
Date recue/Date received 2023-03-31
38
16F). An etch resist 8 is again partially printed onto the thus-generated
second
metal layer 56, which is opaque in this embodiment example, (Fig. 16G) and the
metal layer 56 is removed in the left-open areas 561 by etching (Fig. 16H).
Here
too, the areas 541 and 561 again overlap.
The multilayer body can now be applied to a banknote 7 again by means of an
adhesive layer 57 (Fig. 161). In this embodiment the substrate film 53 is
removed (hot-embossing variant) and no window is provided. The multilayer
body 5 displays the desired effect in the case of direct observation from the
side
of the substrate film 53. As is to be recognized in Fig. 17, the demetalized
area
541 again forms the number "55". The demetalized area 561 forms a frame for
the surface relief 51, which is, however, covered by the metal layer 54. The
oval
shape of the multilayer body can be generated by applying the multilayer body
5
to the banknote 7 by means of hot-embossing with a hot-embossing die
correspondingly shaped to the oval outer contour. The remaining layers of the
multilayer body 5 are peeled off the substrate film 53, and together applied
to
the banknote 7 as a transfer ply, only in the area where the oval hot-
embossing
die acts on the substrate film 53 by means of pressure and heat and activates
the adhesive layer 57 of the multilayer body 5 preferably formed as a heat-
activatable adhesive layer.
A further method for producing a multilayer body 5 with partial demetalization
of
the metal layers is represented in schematic ¨ not to scale ¨ side views in
Figs.
18A to 18G.
An opaque metal layer 58 is also applied here to the substrate film 53 with a
surface relief 51 of the described type. This is overprinted with an etch
resist 8,
which remains omitted in areas to be demetalized. In these areas the metal
layer 58 can then be removed by etching (Fig. 18A). In addition the area of
the
Date recue/Date received 2023-03-31
39
surface relief 51 also initially remains left open here. In this embodiment
the
etch resist 8 is not removed and can take on additional decorative functions.
Next, a first metal layer 54 is applied by vapor deposition under vacuum (Fig.
18B). This first metal layer 54 covers, among other things, the surface relief
51.
This first metal layer 54 is formed semi-transparent in this embodiment
example.
Then the spacer layer 55 is now applied partially and registered relative to
the
surface relief 51 (Fig. 18C) and vapor-deposited over the whole surface with
the
second metal layer 56 (Fig. 16D). This second metal layer 56 is formed opaque.
In areas which are not provided with the partial spacer layer 55, the second
metal layer 56 lies directly on the first metal layer 54. An etch resist 81 is
again
printed onto the thus-generated second metal layer 56, which is opaque in this
embodiment example, partially and registered (Fig. 18E).
The first 54 and the second 56 metal layers are then removed in one step in
the
left-open areas by etching (Fig. 18F). For this, the first 54 and the second
56
metal layers must consist of metals which can be removed with the same
etching solution. Both metal layers preferably consist of the same metal, in
particular preferably both metals consist of aluminum or copper.
The multilayer body 5 can now be applied to a banknote 7 again by means of
an adhesive layer 57 (Fig. 18G). In this embodiment too, the substrate film 53
is
removed (hot-embossing variant) and there is no window. The multilayer body 5
displays the desired effect in the case of direct observation from the side of
the
substrate film. Two demetalizing steps are enough for the method, for this
Date recue/Date received 2023-03-31
40
combined design with metallic areas with e.g. diffractive effects and areas
with
the color tilt effect.
A further method for producing a multilayer body with partial demetalization
of
the metal layers is represented in schematic ¨ not to scale ¨ side views in
Figs.
19A to 19F.
Here too, a semi-transparent metal layer 54 is applied to the substrate film
53
with a surface relief 51 of the described type by vapor deposition under
vacuum
(Fig. 19A). Then the spacer layer 55 is now applied partially and registered
relative to the surface relief 51 (Fig. 19B) and vapor-deposited over the
whole
surface with the second metal layer 56 (Fig. 19C). This second metal layer 56
is
formed opaque. In areas which are not provided with the partial spacer layer
55,
the second metal layer 56 lies directly on the first metal layer 54.
Metallically
diffractive effects are preferably present in these areas. An etch resist 8,
which
remains omitted in areas to be demetalized, is printed onto the second metal
layer 56, which is opaque in this embodiment example, partially and registered
(Fig. 19D). The first 54 and the second 56 metal layers are then removed in
one
step in the left-open areas by etching (Fig. 19E). For this, the first 54 and
the
second 56 metal layers must consist of metals which can be removed with the
same etching solution. Both metal layers preferably consist of the same metal,
in particular preferably both metals consist of aluminum or copper.
The multilayer body 5 can now be applied to a banknote 7 again by means of
an adhesive layer 57 (Fig. 19F). In this embodiment too, the substrate film is
removed (hot-embossing variant) and there is no window. The multilayer body 5
displays the desired effect in the case of direct observation from the side of
the
substrate film. Only one demetalizing step is enough for the method, for this
Date recue/Date received 2023-03-31
41
combined design with metallic areas with e.g. diffractive effects and areas
with
the color tilt effect.
Date recue/Date received 2023-03-31
